I'm based in Wales (UK.
I was hoping for some advice before I started attempting to build my own towable
I recently bought plans from a web site online and the frame seems easy enough
to fabricate but the hydraulics seem so complicated that it has really put me
off. Especially as it seems that the hydraulics make up the majority of the cost.
On further research I have found that I can purchase a used Backhoe (intended
for mounting on a tractor) fairly cheaply.
So, my question is, would is be possible to buy this backhoe, fabricate my own
base and then fit the used backhoe in order to end up with a towable backhoe.
The little towable backhoes and tractor attachment backhoes sort of
work, but they are painfully slow, often can only actuate one joint at a
time and have very little diging power. They have open center hydraulics
with gear pumps of perhaps 10gpm and rarely have more than 20hp driving
By contrast a "real" backhoe has 75-100hp or more driving a high flow
variable displacement piston pump with 30 or more gpm for closed center
hydraulics. Ripping forces are 10,000#+, lift at full extension is a
couple thousand pounds or more, you can operate all four joints at once
in a coordinated fashion and move any joint through it's full travel in
a couple seconds at most.
Buy a used "real" backhoe and refurbish it if you want to do any actual
work with it.
I built a bucket loader for my garden tractor that performed as
designed, inexpensively from mostly used and rebuilt hydraulics. Here
in New England there is snow to plow and a fair amount of excavation
for construction, so the hydraulics business is thriving. Three local
shops helped me with rebuilding and two stores contributed the
fittings. The hoses came from Northern Tool, at a small fraction of
the cost of custom ones.
The design sequence was to roughly estimate what I needed and then
guess on the spot if cheap used components could be repaired and
shoehorned into it. The cylinders are single-acting Porta-Power units
with short strokes that required some geometric gymnastics to leverage
the longer throws I needed. I magically found two 4-ton and two 10-ton
ones in a discount tool store that doesn't normally have used stuff,
for $15 and $20 each. All needed new seals that a nearby shop ordered
for me. The seals were correct only on OD and I had to machine
bushings to adapt them to the pistons. I can see why shops tell me
Chinese cylinders aren't repairable.
Once I had a set of hydraulics I advanced the mechanical design
geometrically, graphically and with a wood mockup to check angles and
clearances, especially for assembly tools and the bulky grease gun.
There's no way I could have done it without a metal lathe and milling
machine. The biggest difficulty was drilling sufficiently parallel
bearing holes in both ends of components longer than my milling
machine's table travel.
Doing it once was a "learning experience."
It would probably have been very expensive to buy hydraulics to fit an
existing mechanical design. While I was in the store a plow operator
came in needing a custom hose similar to one I had paid about $12 for.
He paid $120.
Similarly if I hadn't been free to make changes the pump would have
cost $300 instead of $80, and the valve $150 instead of $40.
I suggest that you thoroughly analyze the maximum forces on all parts
of the backhoe before you modify it. I had to push bearing pressures
beyond the recommendation for Oilite, and made the sleeves from brass
water pipe. I used the moment to lift the back wheels off the ground
as the maximum static load, and just guessed at the max dynamic load
from hitting an obstacle. Actually the front tire sidewalls sprung
leaks before the back came up. Wood crush blocks have prevented
serious collision damage in use. I had to straighten the bucket and
replace one slightly bent pivot pin.
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